In many different manufacturing situations where a number of substantially identical workpieces are to be subjected to a work procedure common to all of the workpieces it is known to provide the workpieces with identically positioned locating features, such as holes and slots, and then during the involved work procedure to support each workpiece in turn on the supporting surface of a table member equipped with a number of pins or other locating devices which mate with the locating features of the workpiece to accurately locate the workpiece relative to the table member. This arrangement allows the workpieces to be quickly placed onto and removed from the table member while yet assuring the accurate placement of each workpiece. It is also known to make one or more of the locating devices used with the table member adjustable to different positions in the plane of the supporting surface to allow the table member and its workpiece locating devices to be set up to accommodate workpieces of different sizes and shapes and with differently positioned work locating features.
The work locating devices used with the table member may in some instances be designed to also aid in holding a workpiece to the supporting surface of the table member, but in many instances the locating devices are used to merely control the position of a workpiece in the plane of the supporting surface, while some other means, such as vacuum openings in the supporting surface of the table member, is used to hold the workpiece vertically in place.
The locating features provided on each workpiece and the complementary locating devices used with the table member may vary widely in shape and size. Commonly, however, the locating features provided on the workpieces are holes and slots and the complementary locating devices used with the table member are cylindrical pins extending upwardly from the supporting surface of the table member. Therefore, in the drawings and in the description and claims which follow the locating features of the workpieces are shown and referred to as holes and slots and the locating devices used with the table member are shown and referred to as pins. These terms should, however, be construed broadly as there is no intention to limit the invention in the broader aspects strictly to holes, slots and pins. Also, the locating devices are shown and described as ones serving to merely position a workpiece in the plane of the supporting surface, but there is likewise no intention to limit the invention to such devices and the invention may be applied as well to locating devices which also aid in holding a workpiece vertically to the supporting surface.
One application of the invention is in the optical inspection of printed circuit boards both in finished and partly finished states where for inspection a circuit board is positioned on the supporting surface of a table member constituting part of an automated optical inspection machine working under computer control. In this and many other applications it is necessary that the workpieces be very accurately located on the supporting surface. It has sometimes been difficult in the past to achieve the desired accuracy because of an adjustable locating unit being somewhat loosely received in a slot of the table member--that is, although the center line of the slot is accurately fixed relative to the supporting surface of the table member, when an adjustable locating unit is moved to a desired position along the length of the slot and then locked in place because of looseness between the locating unit and the slot the locating device portion of the unit may end up being not precisely located on the slot center line as wanted. Also the means for locking the unit in a given position is commonly a set screw carried by the unit and driven against the bottom surface of the slot for locking purposes. This causes marring of the slot bottom surface so that after repeated use of the table it may be difficult to accurately fix the locating unit at a desired position due to the set screw as it is driven onto the slot bottom surface tending to wander into a close-by indentation made in the surface during a previous locking procedure.
The object of the invention is therefore to provide a workpiece locating unit which when used in a complementary T-slot of a table member overcomes the above-mentioned problems by assuring accurate positioning of its locating device on the center line of the slot and which avoids marring of the slot bottom surface by the locking means to allow the unit to be accurately locked at any point along the length of the slot even after the unit has been previously moved to and locked at many different positions along the length of the slot.
Other objects and advantages of the invention will be evident from the following detailed description of preferred embodiments of the invention and from the accompanying drawings and claims.